1. Field of the Invention
The present invention relates to a process for purifying flue gases developed during the incineration of waste materials and containing contaminants including solids of varied compositions, as well as gaseous contaminants, including pollutant gases and heavy metals in gaseous form, wherein flue ash is collected, the flue gas is scrubbed for the purpose of condensing the gaseous contaminants and removing the remaining solids, and the resulting condensate is used to extract soluble heavy metals out of the flue ash. Such a process is disclosed in FRG-OS 3,320,466 and counterpart U.S. Pat. No. 4,617,180, the disclosure of which is herein incorporated by reference.
2. Background of the Art
During flue gas purification, solid, liquid and/or gaseous contaminants are separated from the flue gas with the aim of reducing damage to the environment to an acceptable degree. Contaminant dusts can be separated from flue gas by mechanical and electrical processes, such as passing the flue gas through fabric filters or electrostatic filters, as well as by chemical processes, such as wet dust removal processes employing one or more of an absorption, adsorption, and chemisorption principle. Contaminant gases can be separated from the flue gas by processes including one or more of an absorption, adsorption, condensation, and chemical reaction process. Wet scrubbing processes produce sludges, slurries containing dissolved salts, and waste water, the majority of which generally are not toxic and therefore make decontamination of special refuse unnecessarily expensive and uneconomical.
Flue gas purification systems often combine several of these basic processes into a total process. One of the most common refuse incineration processes provides, at the flue gas end, the purification of the flue gas by removing dust in a filter system including electrostatic or woven filters, and partial removal of the contaminant gases HC1, SO.sub.2, and HF in the flue gas by means of acid or alkali treatment methods upstream or downstream of the filter system. Such a process is described in Abfallwirtschaft an der TU Berlin [Waste Management at the Technical University of Berlin], Volume 7, pages 1-41.
In the past, heavy metals present in gaseous form, e.g., Hg vapor, or organic contaminants, e.g. chlorinated dioxins, have been primarily removed by wet processes downstream of the filters. The removal of heavy metal contaminants, however, has been unreliable and/or inadequate to ensure that the ecosystem is adequately protected, particularly over long-term exposure. High priority problems still remain to be solved with respect to the heavy metal contaminants Hg, Cd, Pb, Sb, Sn, and Zn, as well as others contained in the flue ash, the flue gas and/or the slag from the refuse incineration system.